It is known that bicycles may have internal geared transmissions located in rear hubs. For example, the Shimano Company provides a Shimano Nexus™ eight speed transmission. The transmission comprises an internal geared planetary transmission which is located in a bicycle rear wheel hub. Rohloff GmbH of Germany provides a fourteen speed planetary gear transmission, also for use in a bicycle rear wheel hub.
The prior art transmissions have common disadvantages including heavy weight and that each is located in the bicycle rear wheel hub.
Also representative of the art is U.S. Pat. No. 6,468,178 (2002) to Mohtasham which discloses a rear wheel hub and chainless drive train gear assembly for use on a bicycle having an axle bracket fixed to the frame of the bicycle, a spindle extending axially through the axle bracket and left and right pedal crank arms for rotating the spindle upon application of a pedaling force. A primary drive gear fitted to the spindle drivingly engages carrier gears which operate a planet gear cage housing and a multiple planetary gear and sun gear arrangement according to various gear ratios determined by selective operation of a clutch assembly. Planetary gear groups each include an integral set of planetary gears of varying size which mesh with corresponding sun gear rings. Operation of the clutch assembly serves to selectively engage pawl stops with a corresponding sun gear ring, thereby engaging the corresponding sun gear ring with one of the planetary gears of the planetary gear groups according to a selected gear ratio. The planetary gear groups drive an annular gear ring and an associated annular needle bearing which, in a forward clockwise rotation, engages the hub body to rotate the rear bicycle wheel. Reverse rotation of the annular gear, in a counter-clockwise rotation, results in a freewheeling of the drive train gear assembly relative to the hub body.
What is needed is a planetary gear mechanism comprising a first planetary mechanism connected coaxially in series to a second planetary mechanism, which second planetary mechanism is connected coaxially in series to a third planetary mechanism, the second planetary mechanism output is a step up in speed from the first planetary mechanism output, the third planetary mechanism output is a step up in speed from the second planetary mechanism output. The present invention meets this need.